Electronic equipment such as cellular phone, hard disk drive (HDD), television, or liquid crystal display (LCD) consists of precision parts and electronic elements. The electronic equipment is likely to be broken down or damaged under externally imposed physical impacts and susceptible to external contaminants such as dirt, which interfere air circulation in the electronic equipment to cause overheating of the electronic elements and consequently reduce the life span of the electronic equipment.
To solve these problems, the electronic equipment generally uses polyurethane foam as a material for absorbing external impacts and sealing cracks on the enclosure. Polyurethane foam is a light-weighted porous material excellent in cushioning and sealing properties but very inflammable to cause fast flame spread with great heat dissipation, which adversely affects the electronic equipment, so the electronic equipment after long-term use or in severe environment is likely to ignite when maintained at high temperature for a long time due to heat generation from the electronic elements. For that reason, increasing attention has been directed to the techniques to provide cushioning and sealing sheets with non-flammability.
On the other hand, those materials that are commonly used as a flame retardant comprise halogen-based flame retardant, phosphor-based flame retardant, melamine-based flame retardant, antimony trioxide, or metallic hydroxides. The halogen-based flame retardant generates halogen-based compounds adversely affecting the environment and is not considered as an appropriate flame retardant. Antimony trioxide is also an inappropriate flame retardant due to its adverse effect on the environment. The metallic hydroxides are free from the problem with the halogen-based flame retardant or antimony trioxide in regard to environment. But, a large amount of metallic hydroxides is required to achieve the inherent purpose of the flame retardant, non-flammability, and ends up with a deterioration of the basic properties of the cushioning and sealing sheet.